Screening tests
Basic laboratory screening studies, such as urinalysis and blood studies, can help rule out physiological causes of psychiatric symptoms. Blood studies include complete blood count, erythrocyte sedimentation rate, and the metabolic screening battery (serum electrolyte level, glucose level, and hepatic and renal function tests).
Tests of
endocrine function are particularly important in patients with behavioral symptoms. Patients with depression may have endocrine irregularities, including abnormalities in growth hormone, melatonin, gonadotropin, and thyroid hormone. Patients with
adrenal disorders such as Addison’s disease and Cushing’s syndrome classically demonstrate psychiatric symptoms (see
Chapter 25).
Thyroid function tests are used to screen for hypothyroidism and hyperthyroidism, which can mimic depression and anxiety, respectively. Although no clear association exists between primary depressive illness and abnormal thyroid function, about one-third of depressed patients show decreased thyrotropin response to thyrotropinreleasing hormone. Clearly, thyroid function should be evaluated in depressed patients who also show physical symptoms of hypothyroidism. In a similar way, anxious, agitated patients who also show tremor and weight loss should be evaluated for hyperthyroidism (Joffe 2000).
Table 6-1 provides a summary of laboratory test results for patients with psychiatric symptoms that may be related to physical illnesses. Analysis of blood B
12 and folate levels and a
toxicology screen to identify substance abuse (
Table 6-2) should also be conducted for these patients.
Pharmacotherapy patients
Laboratory tests are used to monitor patients for biological complications of pharmacotherapy (see
Chapter 19). Some psychoactive agents are more likely to cause physical difficulties than others. Specifically, the mood-stabilizing agents,
carbamazepine (Tegretol) and
valproic acid (Depakene, Depakote) are associated with abnormal liver function. Carbamazepine and the antipsychotic agent clozapine (Clozaril) are associated with blood abnormalities such as agranulocytosis (decreased number of granulocytic white blood cells). These abnormalities usually become apparent within the first few months of treatment.
Because they can develop hypothyroidism and kidney problems, patients being treated with the antimanic agent
lithium should have regular T
3, T
4, and TSH, and kidney function (blood urea nitrogen, creatinine, and urinalysis) tests. Because of the drug’s narrow therapeutic range, lithium levels also should be monitored regularly. Plasma concentrations of some antipsychotic and antidepressant agents (e.g., imipramine, desipramine, and nortriptyline) also
may be measured to evaluate patient compliance or to determine whether therapeutic blood levels of the agent have been reached in nonresponding patients.
Measurement of biogenic amines
Altered concentrations of monoamines in neural tissue are involved in the manifestations of major psychiatric disorders (see
Chapter 5). Despite this
close association, it is difficult to correlate directly or predict how changes in these concentrations are associated with changes in behavior. One reason for this is that for practical reasons, levels of monoamines cannot be measured in the brain tissue of living patients. Instead, metabolites of the monoamines, present in higher quantities than the actual monamines, are measured in body fluids such as cerebrospinal fluid, blood, and urine. Although not commonly used in diagnosis, measurement of these metabolites can provide useful clinical and research information about the patient (
Table 6-3).
